This invention relates to machines to apply tape to the leads of lead frames for semiconductor packages so as to secure those leads, which are quite fragile, during processing. Such a machine is described in detail in U.S. Pat. No. 4,193,834. The invention herein comprises an improved mechanism to feed lead frame, particularly lead frame that has already been cut into discrete lengths, into a machine of the type described in that patent. Accordingly, the teachings and drawings of U.S. Pat. No. 4,193,834 are hereby incorporated by reference into this specification and will be referred to from time to time.
When lead frame is supplied in a continuous strip off a reel, such as reel 22 in the earlier referenced patent, it may be advanced by a single mechanism such as the spring loaded pins 206 and 208 that are moved by a carrier block 186 and tilted into holes in the lead frame by a tilt plate 207 in the referenced patent. As therein taught, the strip is clamped during pin retraction and back stroke by a clamp 218. Since the strip is continuous, clamp 218 generally locates the strip along its entire length and guarantees accurate positioning.
However, once one cuts the lead frame into individual discrete strips, which is advantageous for manufacturing reasons, several new problems arise with respect to advancing or indexing these discrete strips into the taping portion of the machine. The indexing mechanism must now engage each and every one of the discrete pieces wherever they are along the feedpath. Also, since each piece is very light, compared to a continuous strip of uncut lead frame, and therefore easily moved, the indexing mechanism must be designed so that it does not itself accidentally nudge the pieces out of position, especially in the taping portion of the machine where accuracy is very important. Still further, the discrete pieces of lead frame advance through the taping portion with spaces between them of unpredictable length. So means must be provided to prevent the application of tape when no lead frame is present in the tape applying portion. The present invention solves these problems.